1. Field of the Invention
The present invention relates generally to an apparatus and a method for controlling operation state of a physical layer. More particularly, the present invention relates to an apparatus and a method for controlling the operation state of IEEE 802.15.4 physical layer by efficiently managing the state of the IEEE 802.15.4 physical layer so as to optimize operations of an upper MAC layer.
2. Description of the Related Art
IEEE 802.15.4 is the standard for specifying a Physical Layer (PHY) and a Media Access Control (MAC) layer and is one of standards for Low Rate Wireless Personal Area Network (LR-WPAN). The IEEE 802.15.4 is established to provide fundamental lower network layers of the WPAN. In particular, the IEEE 802.15.4 aims at low-cost and low-rate ubiquitous communication between devices. It features very low-cost and low-power communication of near devices without underlying communication infrastructure.
While aiming for the distance within 10˜30 m and the transfer rate of about 250 kbit/s, the IEEE 802.15.4 specifies not only the PHY of one type but also various physical layers of different frequencies and modulation/demodulation schemes. Hence, the transfer rate can be divided into 20, 40, and 100 kbit/s.
Various physical layers are supported to address frequency allocation problem among nations and frequency interference problem. An embedded system requiring the low power is to selectively adopt the appropriate physical layer. In particular, the low-power specification can take into account even lower transfer rate.
The unique feature of the IEEE 802.15.4 is the simple technological structure by pursuing the low manufacturing cost. In other words, this feature of the IEEE 802.15.4 pursuits the efficiency through high-level optimization in the implementation.
Main features of the IEEE 802.15.4 protocol include a coordinator having the management function of the WPAN and its connected devices on the function basis. The IEEE 802.15.4 protocol supports two modes; that is, a low-power operation mode of the devices and a time division operation mode for the power management of the entire WPAN including the coordinator. The time division operation includes a function for reserving the guaranteed time lost to suit for real-time applications and a sleep interval of the WPAN for the low-power operations. A basic media access scheme uses collision avoidance using CSMA-CA, and supports a security function through data cryptography. As stated above, the IEEE 802.15.4 exhibits the high-level optimization as the most important feature and requires to get rid of duplication of the functions and the codes for the low-power communication in the implementations of a transceiver chipset and the protocol. To remove error in the operations and to efficiently manage the transceiver, the design for the interface and the operations between the PHY and the MAC layer needs to offer more precise definitions in the implementation than the standard document.
The PHY/MAC interface of the present-day IEEE 802.15.4 WPAN protocol is realized through Application Program Interface (API) using simple transmission and reception functions defined in most transceivers and the embedded state machine. A representative example is TI's CC2420 chip. The CC2420 chip includes a state machine which processes the state corresponding to each function for Tx/Rx according to a designated event when the power is turned on. The code used in the CC2420 chip is redundant and thus the code size is increased and the function of the MAC cannot be optimized. In addition, the MAC protocol in other chips than the corresponding chip cannot be transferred.